1. Field of the Invention
The invention relates to an active pixel sensor device and, in particular, to an active pixel sensor device with different operation modes.
2. Description of Related Art
There are two types of optical sensor devices for fingerprint recognition. One is the passive pixel sensor (PPS) device, and the other is the active pixel sensor (APS) device. In both types of pixel sensor devices, fingerprint recognition is carried out by resetting sensing pixels of the pixel sensor device, exposing the sensing pixels, reading sensing currents of the sensing pixels, and converting the sensing currents into corresponding sensing voltages. However, in addition to the fingerprint recognition function, there are many other optical sensing applications, such as detecting ambient brightness and detecting pulses. The pulse detection is performed by detecting the contraction and expansion of micro blood vessels. The resolution required by such applications is lower than that required by fingerprint recognition.
To integrate the above-mentioned two applications, the optical sensor device usually has an APS device and a photo sensor device. As shown in FIG. 7, the APS device 60 includes an active pixel sensing array 601, a reset and selection circuit 61, and a signal reading circuit 62. Before the active pixel sensing array 601 has an exposure, the reset and selection circuit 61 resets each sensing pixel P11˜Pmn on the active pixel sensing array 601 in sequence, then exposes the active pixel sensing array 601. After the exposure is complete, the reset and selection circuit 61 selects the sensing pixels in a row, and the signal reading circuit 62 reads sensing voltages corresponding to the sensing currents. The photo sensor device 70 includes a photo sensing array 701 and a signal reading circuit 72. The sensing pixels of the photo sensor array 701 have a relative larger photo sensing area. Therefore, after the photo sensor array 701 is reset and exposed, the sensing current detected by the signal reading circuit 72 is converted into a corresponding sensing voltage. The sensing voltage is used to determine the intensity of the ambient brightness or the variation in the contraction and expansion of micro blood vessels on a finger.
Accordingly, to integrate two or more different applications, the optical sensor device has to use two different sensors, such as the active pixel sensing array 601 and the photo sensing array 701. Moreover, the two different sensing arrays have different circuit designs, and result in increasing both the cost and size of the entire device. In the example of having fingerprint recognition and pulse measurements, the user needs to place his finger on different regions corresponding to the different sensors for different purposes. Such operation is not convenient and needs to be improved.